MAX8790AETP+;MAX8790AETP+T;中文规格书,Datasheet资料

19-0989;Rev0;10/07

ONKI

T

EVALUATIBLE

AVAILASix-StringWhiteLEDDriverwithActive

CurrentBalancingforLCDPanelApplications

MAX87

GeneralDescription

Features

TheMAX8790Aisahigh-efficiencydriverforwhitelight-oDrivesSixParallelStringswithMultipleSeries-

emittingdiodes(LEDs).Itisdesignedforlargeliquid-ConnectedLEDsperString

crystaldisplays(LCDs)thatemployanarrayofLEDsaso±1.5%CurrentRegulationAccuracyBetween

thelightsource.Acurrent-modestep-upcontrollerdrives

Strings

uptosixparallelstringsofmultipleseries-connected

LEDs.Eachstringisterminatedwithballastthatachieves

±1.5%currentregulationaccuracy,ensuringevenbright-

oLow450mVFeedbackVoltageatFullCurrent

ImprovesEfficiency

nessforallLEDs.TheMAX8790Ahasawideinput-volt-oStep-UpControllerRegulatestheOutputJust

agerangefrom4.5Vto26V,andprovidesafixed20mA

oradjustable15mAto27mAfull-scaleLEDcurrent.

AbovetheHighestLEDStringVoltage

oFull-ScaleLEDCurrentAdjustablefrom15mAto

27mA,orPreset20mA

TheMAX8790Ahastwodimmingcontrolmodesto

enableawidevarietyofapplications.IndirectDPWM

oWide100:1DimmingRange

mode,theLEDcurrentisdirectlyturnedonandoffbya

PWMsignal.Inanalogdimmingmode,aninternal

phase-lockedloop(PLL)circuittranslatesthePWMsig-

oProgrammableDimmingControl:DirectDPWMor

AnalogDimming

nalintoananalogsignalandlinearlycontrolstheLED

currentdownto12.5%.Below12.5%,digitaldimmingis

oBuilt-InPLLforSynchronizedDimmingControl

oOpenandShortLEDProtections

Bothcontrolmethodsprovide100:1dimmingrange.addedtoallowloweraverageLEDcurrentdownto1%.oOutputOvervoltageProtection

oWideInputVoltageRangefrom4.5Vto26V

TheMAX8790Ahasmultiplefeaturestoprotectthecon-

trollerfromfaultconditions.SeparatefeedbackloopslimitoExternalMOSFETAllowsaLargeNumberofLEDs

theoutputvoltageifoneormoreLEDsfailopenorshort.perString

Thecontrollerfeaturescycle-by-cyclecurrentlimittopro-

o500kHz/750kHz/1MHzSwitchingFrequency

videconsistentoperationandsoft-startcapability.Ather-

mal-shutdowncircuitprovidesanotherlevelofprotection.

oSmall,20-Pin,4mmx4mmThinQFNPackage

Thestep-upcontrollerusesanexternalMOSFET,which

providesgoodefficiencyandallowsforscalableoutput

SimplifiedOperatingCircuit

powerandmaximumoperatingvoltage.Lowfeedback

voltageateachLEDstring(450mV)helpsreduce

powerloss.TheMAX8790Afeaturesselectableswitch-V

ingfrequency(500kHz,750kHz,or1MHz),which

L1

D1

VOUT

IN

C

allowstrade-offsbetweenexternalcomponentsizeand

ope-ratingefficiency.

IN

0.1μF

TheMAX8790Aisavailableinathermallyenhanced,

lead-free,20-pin,4mmx4mm,ThinQFNpackage.

IN

SHDN

EXT

CS

N1

VCC

FSET

Applications

ISET

Rs

Notebook,Subnotebook,andTabletComputer

Displays

MAX8790A

GND

OV

BRT

R1

AutomotiveSystems

HandyTerminals

N.C.

N.C.

OSC

R2

CPLL

CCV

OrderingInformation

FB1

FB2

FB3

FB4

FB5

FB6

ENA

EP

PKG

PART

TEMPRANGE

PIN-PACKAGE

CODE

-40°Cto+85°C20ThinQFN

(4mmx4mm)

MAX8790AETP+

T2044-3

+Denotesalead-freepackage.

PinConfigurationappearsatendofdatasheet.

________________________________________________________________

MaximIntegratedProducts1

Forpricing,delivery,andorderinginformation,pleasecontactMaximDirectat1-888-629-4642,

orvisitMaxim’swebsiteat.

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Six-StringWhiteLEDDriverwithActive

CurrentBalancingforLCDPanelApplications

A

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9

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ABSOLUTEMAXIMUMRATINGS

IN,SHDN,toGND.................................................-0.3V

FB_toGND............................................................-0.3V

VCC,BRT,ENA,OSC,OVtoGND...........................-0.3VStor+6VageTemperatureRange.............................-60°Cto+150°C

ISET,CCV,CS,FSET,CPLL,EXTtoGND.-0.3VtoCC(V+0.3V)

ContinuousPowerDissipationA(T=+70°C)

20-PinThinQFN(derate16.9mW/°Cabove+70°C)...1349mW

OperatingTtoemp+28VeratureRange...........................-40°Cto+85°C

JunctionTempertoatu+28Vre...................................................

LeadTemperature(soldering,10s).................................+300°

Stressesbeyondthoselistedunder“AbsoluteMaximumRatings”maycausepermanentdamagetothedevice.Thesearestressratingsonly,andfunctional

operationofthedeviceattheseoranyotherconditionsbeyondthoseindicatedintheoperationalsectionsofthespecificationsisnotimplied.Exposur

absolutemaximumratingconditionsforextendedperiodsmayaffectdevicereliability.

ELECTRICALCHARACTERISTICS

(CircuitofFigureIN1.=V12V,VSHDN=VIN,CCV=0.1µF,TA=0°Cto+85°C,unlessotherwisenoted.TypicalvaluesareA=at+2T5°C.)

PARAMETER

CONDITIONS

MIN

4.5

5.5

TYP

MAX

UNITS

V

VIN=VCC

VCC=bypassedtoGNDthrough1µFcapacitor

5.5

INInputVoltageRange

26.0

2

VIN=26V

1

1

VSHDN=high,

BRT=GND

mA

INQuiescentCurrent

VIN=VCC=5V

2

SHDN

=GND

10

µA

V

VCCOutputvoltage

VCCShort-CircuitCurrent

VCCUVLOThreshold

STEP-UPCONVERTER

VSHDN=5V,6V<INV<26V,0<VCCI<10mA

4.7

15

5.0

56

5.3

130

4.45

mA

V

Risingedge,hysteresis=20mV

4.00

4.25

VCC-

0.1

EXTHighLevel

10mAfromEXTtoGND

VCC

V

EXTLowLevel

-10mAfromEXTtoVCC

EXThighorlow

0

2

1

0.1

5

V

EXTOn-Resistance

EXTSink/SourceCurrent

Ω

A

EXTforcedto2V

VCC

0.4

-

OSCHigh-LevelThreshold

V

V

VCC-

2.0

OSCMidlevelThreshold

OSCLow-LevelThreshold

1.5

0.4

1.1

825

550

V

VOSC=VCC

0.9

675

450

1.0

750

500

10

MHz

OperatingFrequency

VOSC=open

VOSC=GND

kHz

%

PWMmode

MinimumDutyCycle

Pulseskipping,noload

0

MaximumDutyCycle

CSTripVoltage

94

85

95

%

Dutycycle=75%

100

115

mV

CONTROLINPUT

SHDNLogic-InputHighLevel

2.1

2.1

V

V

V

V

SHDN

Logic-InputLowLevel

0.8

0.8

BRT,ENALogic-InputHighLevel

BRT,ENALogic-InputLowLevel

2

_______________________________________________________________________________________

/

Six-StringWhiteLEDDriverwithActive

CurrentBalancingforLCDPanelApplications

MAX87

ELECTRICALCHARACTERISTICS(continued)

(CircuitofFigureIN1.=V12V,VSHDN=VIN,CCV=0.1µF,TA=0°Cto+85°C,unlessotherwisenoted.TypicalvaluesareA=at+2T5°C.)

PARAMETER

CONDITIONS

MIN

TYP

MAX

UNITS

INPUTLEAKAGE

LeakageCurrent

SHDN

SHDN

=26V

+42

+50

+3

μA

μA

μA

μA

μA

μA

CSLeakageCurrent

OSCLeakageCurrent

BRT,ENALeakageCurrent

FSET,ISETLeakageCurrent

OVLeakageCurrent

LEDCURRENT

VCS=GND

+40

-3

-1

+1

FSET=ISET=VCC

-1

+1

-0.1

+0.1

ISET=VCC,BRT=100%

19.40

24.25

14.40

20.00

25.00

20.60

25.75

Full-ScaleFB_OutputCurrentRISET=80ktoGND,BRT=100%

RISET=133ktoGND,BRT=100%

mA

15.0015.60

VCC-

0.4

ISETHigh-LevelThreshold

Defaultsettingfor20mAfull-scaleLEDcurrent

V

ISETVoltage

1.121.191.26

V

mA

%

20%OutputCurrent

ISET=VCC,BRT=20%

3.84

-1.5

-2.0

300

4.00

4.16

+1.5

+2.0

800

720

500

200

20

ISET=VCC,BRT=100%

CurrentRegulationBetween

Strings

ISET=VCC,BRT=20%

%

RISET=80ktoGND,BRT=100%

ISET=VCC,BRT=100%

500

450

275

120

13

MinimumFB_Regulation

Voltage

270

mV

ISET=VCC,12.5%

150

MaximumFB_Ripple

FB_On-Resistance

ISET=VCC,COUT=1μF,OSC=CCV(Note1)

VFB_=50mV

mVP-P

SHDN=GND,VFB_=26V

SHDN=VIN,BRT=GND,VFB_=15V

1

FB_LeakageCurrent

μA

10

28

BRTInputFrequency

MinimumBRTDutyCycle

FAULTPROTECTION

100

500

Hz

%

PLLactive

12.5

1.23

OVThresholdVoltage

1.16

1.30

V

V

VCC+VCC+VCC+

0.20

FB_OvervoltageThreshold

0.6

1.45

FAULTShutdownTimer

Thermal-ShutdownThreshold

PHASE-LOCKEDLOOP

VFB_>5.6V(typ)

(Note1)

50

65

80

ms

170

°C

VCC-

0.4

FSETHigh-LevelThreshold

BRTFrequencyCaptureRange

PLLdisabled

V

RFSET=500k

RFSET=250k

150200250

300400500

Hz

_______________________________________________________________________________________

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Six-StringWhiteLEDDriverwithActive

CurrentBalancingforLCDPanelApplications

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ELECTRICALCHARACTERISTICS

(CircuitofFigureIN1.=V12V,VSHDN=VIN,CCV=0.1µF,TA=-40°Cto+85°C,unlessotherwisenoted.)(Note2)

PARAMETER

CONDITIONS

MIN

TYP

MAX

UNITS

V

VIN=V4.5

CC

5.5

INInputVoltageRange

VCCbypassedtoGNDthrough1μFcap

5.5

26.0

2

VIN=26V

V

=high

mA

BRT=GND

INQuiescentCurrent

VIN=VCC=5V

2

=GND

=5V,6V<INV<26V,0<VCCI<10mA

10

μA

V

VCCOutputVoltage

V

4.7

12

5.3

130

4.45

VCCShort-CircuitCurrent

VCCUVLOThreshold

STEP-UPCONVERTER

mA

V

Risingedge,hysteresis=20mV

4.00

VCC-

0.1

EXTHighLevel

10mAfromEXTtoGND

V

V

EXTLowLevel

-10mAfromEXTtoVCC

EXThighorlow

0.1

5

V

V

EXTOn-Resistance

VCC-

0.4

OSCHigh-LevelThreshold

VCC-

2.0

OSCMidlevelThreshold

OSCLow-LevelThreshold

1.5

0.4

1.1

825

550

V

VOSC=VCC

VOSC=open

VOSC=GND

0.9

M

Hz

OperatingFrequency

675

450

94

kHz

MaximumDutyCycle

CSTripVoltage

%

Dutycycle=75%

85

115

mV

CONTROLINPUT

Logic-InputHighLevel

Logic-InputLowLevel

BRT,ENALogic-InputHigh

2.1

V

V

V

V

0.8

0.8

2.1

BRT,ENALogic-InputLowLevel

INPUTLEAKAGE

LeakageCurrent

=26V

+42

+50

+3

μA

μA

μA

μA

μA

μA

CSLeakageCurrent

VCS=GND

OSCLeakageCurrent

BRT,ENALeakageCurrent

FSET,ISETLeakageCurrent

OVLeakageCurrent

-3

-1

+1

FSET=ISET=VCC

-1

+1

-0.1

+0.1

4

_______________________________________________________________________________________

/

Six-StringWhiteLEDDriverwithActive

CurrentBalancingforLCDPanelApplications

MAX87

ELECTRICALCHARACTERISTICS(continued)

(CircuitofFigureIN1.=V12V,VSHDN=VIN,CCV=0.1µF,TA=-40°Cto+85°C,unlessotherwisenoted.)(Note2)

PARAMETER

CONDITIONS

MIN

TYP

MAX

UNITS

LEDCURRENT

ISET=VCC,BRT=100%

19.2

24.0

14.4

20.8

26.0

15.6

Full-ScaleFB_OutputCurrentRISET=80kΩtoGND,BRT=100%

RISET=133kΩtoGND,BRT=100%

mA

V

VCC-

0.4

ISETHigh-LevelThreshold

Defaultsettingfor20mAfull-scaleLEDcurrent

ISETVoltage

1.12

3.8

-2

1.26

4.2

+2

V

20%OutputCurrent

ISET=VCC,BRT=20%

mA

ISET=VCC,BRT=100%

ISET=VCC,BRT=20%

CurrentRegulationBetween

Strings

%

-3

+3

RISET=80kΩtoGND,BRT=100%

280

250

140

840

760

530

200

20

MinimumFB_RegulationVoltageISET=VCC,BRT=100%

ISET=VCC,BRT=12.5%

mV

MaximumFB_Ripple

FB_On-Resistance

ISET=VCC,COUT=1µF,OSC=CCV(Note1)

mVP-P

Ω

VFB_=50mV

SHDN=GND,VFB_=26V

SHDN=VIN,BRT=GND,VFB_=15V

1

FB_LeakageCurrent

µA

28

BRTInputFrequency

FAULTPROTECTION

100

500

Hz

OVThresholdVoltage

1.16

1.30

V

V

VCC

+

VCC+

1.45

FB_OvervoltageThreshold

0.2

FAULTShutdownTimer

PHASE-LOCKEDLOOP

VFB_>5.6V(typ)

PLLdisabled

50

80

ms

VCC-

0.4

FSETHigh-LevelThreshold

BRTFrequencyCaptureRange

V

RFSET=500kΩ

RFSET=250kΩ

150

300

250

500

Hz

Hz

Note1:Specificationsareguaranteedbydesign,notproductiontested.

Note2:Specificationsto-40°Careguaranteedbydesign,notproductiontested.

_______________________________________________________________________________________

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Six-StringWhiteLEDDriverwithActive

CurrentBalancingforLCDPanelApplications

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TypicalOperatingCharacteristics

(CircuitconfigurationIN1,=V12V,VSHDN=VIN,LEDs=8seriesx6parallelstrings,ISETCC,=TAV=+25°C,unlessotherwisenoted.)

BOOSTCONVERTEREFFICIENCY

vs.INPUTVOLTAGE(BRT=100%)

NORMALIZEDPOWERvs.TOTALLEDCURRENT

(ANALOGANDDPWMDIMMING)

LEDCURRENTvs.BRTDUTYCYCLE

(BRTAT200Hz)

94

1.2

25

20

15

10

5

1

NORMALIZEDTOIVN=20V,ANLDEDI=20mA

2

0

c

o

IDENTICALFORDPWMDIMMING

ANDANALOGDIMMING

3

0

c

o

0

c

o

t

A

0

9

7

8

X

A

M

VIN=7V

t

A

0

9

7

8

X

A

M

t

A

0

9

7

8

X

A

M

)93

%

1.0

(

500kHz

Y

C

N

E

92

91

90

89

88

87

86

R

)

A

E

I

C

W0.8

m

750kHz

I

F

O

P

(

T

N

E

R

R

U

C

D

E

L

TOTALINPUT

POWER,ANALOG

F

E

D

R

E

T

R

E

V

N

O

C

E

0.6

0.4

0.2

0

Z

I

L

A

M

TOTALLED

POWER,DPWM

POWER,DPWM

R

O

N

TOTALINPUT

1MHz

T

S

O

O

B

TOTALLED

POWER,ANALOG

0

7

12

17

1

10

100

1000

1

10

100

INPUTVOLTAGE(V)

TOTALLEDCURRENT(mA)

BRTDUTYCYCLE(%)

LEDCURRENT

vs.AMBIENTTEMPERATURE(BRT=100%)

LEDCURRENTREGULATION

vs.INPUTVOLTAGE

FB_VOLTAGEvs.LEDCURRENT

(ANALOGDIMMING)

21.0

0.05

0.04

0.03

0.02

0.01

0

0.7

0.6

4

0

c

o

t

A

0

9

7

8

X

A

M

5

0

c

o

t

A

0

9

7

8

X

A

M

6

0

c

o

t

A

0

9

20.8

20.6

)

%

7

X8

)

V

(

E

(

N

O

A

M

DPWMDIMMING

BRT=10%

G0.5

)20.4

A

I

T

A

T

L

O

m

A

L

U

G

E

R

(

T

N

E

20.2

V

0.4

N

O

R20.0

R

U

I

T

T

N

E

R

R

A0.3

C

19.8

-0.01

L

U

G

E

D

E

DPWMDIMMING

BRT=100%

L19.6

19.4

U-0.02

C

R

0.2

_

B

F

D

E-0.03

L

-0.04

ANALOGDIMMING

BRT=10%

0.1

0

19.2

19.0

-0.05

0

20

40

60

80

7

12

17

0

5

10

15

20

25

30

AMBIENTTEMPERATURE(°)

INPUTVOLTAGE(V)

LEDSTRINGCURRENT(mA)

SUPPLYCURRENTvs.INPUTVOLTAGE

(DPWMDIMMING)

SWITCHINGWAVEFORMS

(BRT=100%)

SHUTDOWNCURRENTvs.INPUTVOLTAGE

7

6

7

MAX8790Atoc09

7

0

c

o

t

8

0

c

o

t

A

0

9

7

8

X

A

M

6

A

90

7

8

X

A

M

)

A

)

μ

(

A

m

VLX

10V/div

5

4

3

2

1

0

5

4

3

2

1

0

T

(

T

N

E

R

R

U

C

Y

L

P

P

U

S

BRT=100%

N

E

R

R

U

C

0V

N

W

O

D

T

U

H

S

BRT=0%

I

L

500mA/div

0mA

7

12

17

7

12

17

200ns/div

INPUTVOLTAGE(V)

INPUTVOLTAGE(V)

6

_______________________________________________________________________________________

/

Six-StringWhiteLEDDriverwithActive

CurrentBalancingforLCDPanelApplications

MAX87

TypicalOperatingCharacteristics(continued)

(CircuitconfigurationIN1,=V12V,VSHDN=VIN,LEDs=8seriesx6parallelstrings,ISETCC,=TAV=+25°C,unlessotherwisenoted.)

SWITCHINGWAVEFORMS

(BRT=15%,ANALOGDIMMING)

MAX8790Atoc10

STARTUPWAVEFORMS

(BRT=100%,DPWMDIMMING)

LEDCURRENTWAVEFORMS

(BRT=50%AT200Hz,DPWMDIMMING)

MAX8790Atoc12

MAX8790Atoc11

SHDN

5V/div

BRT

5V/div

0V

0V

VFB1

5V/div

VLX

10V/div

VOUT

0V20V/div

0V

0V

I

100mA/div

VCCV

LED

0V2V/div

0mA

0A

I

L

500mA/div

0mA

I

1A/div

I

1A/div

L

L

0A

1μs/div

4ms/div

2ms/div

LEDCURRENTWAVEFORMS

(BRT=1%AT200Hz,DPWMDIMMING)

MAX8790Atoc13

LEDCURRENTWAVEFORMS

(BRT=50%AT200Hz,ANALOGDIMMING)

MAX8790Atoc14

BRT

5V/div

BRT

5V/div

0V

0V

0V

VFB1

5V/div

VFB1

1V/div

0V

I

100mA/div

I

50mA/div

LED

LED

0mA

0A

0mA

I

1A/div

I

1A/div

L

L

0A

1ms/div

1ms/div

LEDCURRENTWAVEFORMS

(BRT=1%AT200Hz,ANALOGDIMMING)

LED-OPENFAULTPROTECTION

(BRT=100%,LEDOPENONFB3)

MAX8790Atoc16

MAX8790Atoc15

BRT

5V/div

VFB3

1V/div

0V

0V

0V

0V

VFB1

2V/div

VFB1

10V/div

I

50mA/div

VOUT

20V/div

LED

0mA

0V

I

500mA/div

I

1A/div

L

L

0mA

0A

1ms/div

20ms/div

_______________________________________________________________________________________

7

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Six-StringWhiteLEDDriverwithActive

CurrentBalancingforLCDPanelApplications

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TypicalOperatingCharacteristics(continued)

(CircuitconfigurationIN1,=V12V,VSHDN=VIN,LEDs=8seriesx6parallelstrings,ISETCC,=TAV=+25°C,unlessotherwisenoted.)

LED-SHORTFAULTPROTECTION

(BRT=100%,2LEDsSHORTONFB3)

MAX8790Atoc17

LEDCURRENTBALANCING

vs.INPUTVOLTAGE(BRT=100%)

1.00

0.90

0.80

0.70

0.60

0.50

0.40

VFB3

1V/div

)

%

8

1

c

o

t

A

0

9

7

8

X

A

M

(

Y

C

A

R

U

C

C

A

0V

VFB1

10V/div

0V

G

N

I

C

1MHz

N

A

L

A

B

VOUT

20V/div

0V

T

N0.30

E

R

R

500kHz

I

1A/div

L

0.20

0.10

0

U

C

0A

D

E

L

750kHz

10ms/div

7

12

17

INPUTVOLTAGE(V)

PinDescription

PIN

1

NAME

OSC

FUNCTION

OscillatorFrequencySelectionPin.ConnectOSCtoVCCtosetthestep-upconverter’soscillatorfrequencyto

1MHz.ConnectOSCtoGNDtosettheefrquencyto500kHz.FloatOSCtosettheeqfruencyto750kHz.

AnalogDimmingEnable.ENAsetstheWPMcontrolmode.SetENALOWtoenabledirectDPWMdimming.

SetENAHIGHtoenableanalogdimming.Inbothmodes,theudtycycleoftheWPMsignalattheBRTniput

controlstheLEDcurrentcharacteristics.SeetheDimmingControlsectionforacompletedescription.

2

3

ENA

BRT

BrightnessControlInput.ThedutycycleofthisdigitalinputsignalcontrolstheLEDcurrentcharacteristics

Theallowablefrequencyrangeis100Hzto500Hzinanalogdimmingmode.Thedutycyclecanbe100%

to1%.TheBRTfrequencycangoabove500HzindirectDPWMmodeaslongastheBRTpulsewidthis

greaterthan50µsminimum.SeetheDimmingControlsectionforacompletedescription.

ShutdownControlInput.TheMAX8790AshutsdownwhenSHDNislessthan0.8V.PullingSHDN

2.1VenablestheMAX8790A.SHDNcanbeconnectedtotheinputvoltageifdesired.

above

4

5

6

SHDN

FB1

LEDString1CathodeConnection.FB1istheopen-drainoutputofaninternalregulator,whichcontrols

currentthroughFB1.FB1cansinkupto27mA.Ifunused,connectFB1toGND.

LEDString2CathodeConnection.FB2istheopen-drainoutputofaninternalregulator,whichcontrols

currentthroughFB2.FB2cansinkupto27mA.Ifunused,connectFB2toGND.

FB2

LEDString3CathodeConnection.FB3istheopen-drainoutputofaninternalregulator,whichcontrols

currentthroughFB3.FB3cansinkupto27mA.Ifunused,connectFB3toGND.

7

8

9

FB3

GND

FB4

Ground

LEDString4CathodeConnection.FB4istheopen-drainoutputofaninternalregulator,whichcontrols

currentthroughFB4.FB4cansinkupto27mA.Ifunused,connectFB4toGND.

LEDString5CathodeConnection.FB5istheopen-drainoutputofaninternalregulator,whichcontrols

currentthroughFB5.FB5cansinkupto27mA.Ifunused,connectFB5toGND.

10

FB5

8

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/

Six-StringWhiteLEDDriverwithActive

CurrentBalancingforLCDPanelApplications

MAX87

PinDescription(continued)

PIN

11

NAME

FB6

FUNCTION

LEDString6CathodeConnection.FB6istheopen-drainoutputofaninternalregulator,whichcontrols

currentthroughFB6.FB6cansinkupto27mA.Ifunused,connectFB6toGND.

Step-UpControllerCurrent-SenseInput.ConnecttheCSinputtoaground-referencedsenseresistorto

measurethecurrentintheexternalMOSFETswitch.

12

13

14

CS

EXT

OV

ExternalMOSFETGate-DriveOutput

OvervoltageSense.ConnectOVtothecentertapofaresistivevoltage-dividerOUTfromtogVround.The

detectionthresholdforvoltagelimitingatOVis1.23V(typ).

5VLinearRegulatorOutput.CCVprovidespowertotheMAX8790Aandisalsousedtobiasthegatedriver

fortheexternalMOSFET.BypassCCVtoGNDwithaceramiccapacitorof1µForgreater.INiIfslVess

thanorequalto5.5V,connectCCVtoINtothedisabletheinternalLDOandusetheexternal5Vsupplyto

VCC.WhenSHDNislow,theinternallinearregulatorisdisabled.

15

VCC

SupplyInput.INVbiasestheinternal5Vlinearregulatorthatpowersthedevice.BypassINtoGNDdirectly

atthepinwitha0.1µForgreaterceramiccapacitor.

16

17

IN

Step-UpConverterCompensationPin.Connecta0.1µFceramiccapacitorandΩ1.2kresistorfromCCVto

GND.WhentheMAX8790Ashutsdown,CCVisdischargedto0Vthroughaninternal20kΩresistor.

CCV

Full-ScaleLEDCurrentAdjustmentPin.TheresistancefromISETtoGNDcontrolsthefull-scalecurrentin

eachLEDstring:

18

19

ISET

FSET

I

=20mAx100kΩ/RISET

LEDmax

Theacceptableresistancerangeis74kΩ<RISET<133kΩ,whichcorrespondstofull-scaleLEDcurrentof

27mA>ILEDmax>15mA.ConnectISETtoVCCforadefaultfull-scaleLEDcurrentof20mA.

PLLFree-RunningFrequencyControlPin.TheresistancefromFSETtoGNDcontrolsthePLLoscillator’s

free-runningfrequency,PLLf:

f=1/(10xRx800pF)

PLL

FSET

Thecapturerangeis0.6PLLxftoPLLf.TheacceptableresistancerangeforFSETisΩ250k<RFSET

754kΩ,whichcorrespondstoafrequencyrangeof500HzPLL>f>166Hz.Theresultingcapture

frequencyrangeis100Hzto500Hz.

<

Phase-LockedLoop-CompensationCapacitorPin.ThecapacitanceatCPLLcompensatesthePLLloop

response.Connecta0.1µFceramiccapacitorfromCPLLtoGND.

20

EP

CPLL

EP

ExposedBacksidePad.Soldertothecircuitboardgroundplanewithsufficientcopperconnectionto

ensurelowthermalresistance.SeethePCBLayoutGuidelinessection.

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9

/

Six-StringWhiteLEDDriverwithActive

CurrentBalancingforLCDPanelApplications

A

0

9

7

8

X

A

M

DetailedDescription

aredirectlyturnedonandoffbythePWMsignal.Inana-

logdimmingmode,aninternalPLL,digitalcomparator,

andDACcircuittranslatethePWMsignalintoananalog

signalthatlinearlycontrolstheLEDcurrent,downtoa

TheMAX8790Aisahigh-efficiencydriver